In the course of this fiscal year, we have worked on the soluble systems described in the following paragraphs, which constitute attractive targets for the development of pharmaceutical agents. Human cytidine deaminase. Cytidine deaminase (CDA) is a cytosolic enzyme which catalyzes the hydrolytic deamination of cytidine to uridine. CDA causes the degradation of several cytidine based compounds potentially active as anticancer or antiviral agents. Glutamate carboxypeptidase II. Glutamate carboxypeptidase II (GCPII) is an enzyme that catalyzes the hydrolysis of N-acetylaspartylglutamate (NAAG) to N-acetylaspartate and glutamate. Its inhibitors have the potential of being applied to the treatment of prostate cancer or brain stroke, depending on their ability of crossing the blood-brain barrier. Giardia lamblia actin. Inhibitors of Giardia lamblia actin have the potential of providing a novel therapeutic strategy to prevent the attachment of this parasite to the host. However, most of the currently known actin inhibitors are natural toxins that act more potently at the mammalian proteins rather than at the parasite, while, for a pharmaceutical application, the opposite would be required. In particular, during this fiscal year, we have conducted the research and accomplished the results described in the following paragraphs. 1) Developed a computational model for the prediction of passive blood-brain partitioning. We developed this model in order to select, among the potential GCPII inhibitors suggested by a virtual screening that we conducted last year, those that are more likely to access the brain. Notably, however, this effective model can be generally applied to the study of any organic compound and drug candidate. 2) Continued our virtual screening efforts for the identification of GCPII inhibitors capable to cross the blood brain barrier, to be used in the treatment of neurological diseases. The discovery of structural diverse ligands would also allow us to solve new crystal structures, thus furthering our understanding of the plasticity of this enzyme. Experimental collaborators: Prof. Joseph Neale (Department of Biology, Georgetown University) 3) Completed a virtual screening for the identification of CDA inhibitors and identified several active compounds. Experimental collaborators: Prof. Alberto Vita (University of Camerino, Italy). 4) Rationalized the role of a specific amino acid residue (Tyr 33) in the stabilization of the CDA quaternary structure, through the combination of molecular modeling and biochemical experiments. Experimental collaborators: Prof. Alberto Vita (University of Camerino, Italy). 5) Continued the studies on the structure-function relationships of CDA. Experimental collaborators: Prof. Alberto Vita (University of Camerino, Italy). 6) Studied similarities and differences between human and Giardia actin. The insights generated from this study will be fundamental for our search for compounds capable of selectively perturbing the attachment of Giardia actin without interfering with the human protein.